A red mud-graphite tailings road base material and a preparation method thereof

Abstract

The present application belongs to the technical field of solid waste treatment, and particularly relates to a kind of alkali-proof red mud-graphite tailings road base material and preparation method thereof.The red mud-graphite tailings road base material includes the following components by weight: 30-45 parts of red mud, 55-70 parts of graphite tailings, 2-3 parts of P·O 42.5 Portland cement, 3-6 parts of slag powder, 8-10 parts of phosphogypsum, 0.1-0.3 parts of polycarboxylate superplasticizer, 0.01-0.03 parts of modified MIL-101(Fe)-NH2, and 12-15 parts of water;The particle size of the graphite tailings is in the range of 7.5-11.2 mm, and the particle size of the red mud is ≤5 mm.The road base material not only solves the problem of heavy metal pollution existing in red mud-graphite tailings base material, but also effectively solves the problem that red mud-graphite tailings base material easily leads to alkali efflorescence of road base.

Description

Technical Field

[0001] This invention belongs to the technical field of concrete materials, specifically relating to a red mud-graphite tailings road base material with anti-efflorescence properties and its preparation method. Background Technology

[0002] Red mud is a highly alkaline industrial waste generated during the alumina production process. It contains a significant amount of sodium (Na) alkaline components, as well as heavy metal pollutants such as lead (Pb), chromium (Cr), and arsenic (As), especially lead. Lead in red mud can migrate and accumulate significantly in the soil at a depth of 0-60 cm via leachate, primarily existing in a reducible form with extremely high potential for migration. Therefore, the remediation of heavy metal pollution in red mud, especially lead pollution, is urgently needed.

[0003] Graphite tailings are industrial waste generated during the process of refining graphite from graphite ore. The heavy metal elements in them can cause soil pollution, and the exposure of graphite tailings to the atmosphere can also cause dust pollution. Therefore, the resource utilization of graphite tailings is urgently needed.

[0004] Current technologies utilize red mud and graphite tailings together as road base materials, which has become a major direction for the high-value utilization of solid waste, with significant ecological and economic benefits.

[0005] However, red mud-graphite tailings-based road base materials have the following defects: The strong alkalinity of red mud easily leads to efflorescence, a common salt precipitation problem in road engineering. The efflorescence crystals form a loose salt film between the base layer and the asphalt surface layer, damaging the bonding interface and causing defects such as voids, displacement, and cracking in the surface layer, thereby weakening the interlayer adhesion. The crystallization of salts generates volume expansion pressure, and repeated crystallization-dissolution cycles reduce the adhesion between aggregate particles in the base layer surface, resulting in surface loosening and pulverization, reducing the load-bearing capacity of the base layer, and subsequently causing pulverization and spalling of the base layer surface. Furthermore, the moisture carried by efflorescence freezes and expands at low temperatures, which, combined with the expansion from salt crystallization, accelerates freeze-thaw damage to the base layer structure.

[0006] In addition, the road base material based on red mud-graphite tailings uses red mud containing heavy metals, so it is necessary to effectively solidify the heavy metals in such road base materials.

[0007] Patent CN116924740A discloses a red mud-graphite tailings road base material, its preparation method, and its application. The base material comprises the following components in parts by weight: 0.05-0.07 parts of ionomer curing agent (ISS), 0.0012-0.0015 parts of early strength agent, 0.25-0.35 parts of anti-hard water agent, 4-5 parts of cement, 60 parts of gravel, 5-20 parts of red mud, 5-20 parts of graphite tailings, 0-30 parts of stone chips, and 5-7 parts of water; the particle size range of the gravel is 5-20 mm; the particle size of the red mud and graphite tailings is ≤5 mm; the particle size of the stone chips is ≤5 mm; the ISS is sodium ricinoleate sulfate, the early strength agent is triethanolamine, and the anti-hard water agent is sodium dodecyl diphenyl ether disulfonate; the 7-day unconfined compressive strength range of the red mud-graphite tailings road base material is 5.3-6.8 MPa. The curing agent ISS (sodium ricinoleate sulfate) used in this method mainly relies on ion exchange and surface complexation, lacking stable chemical bonding for the fixation of heavy metals. Under service environments such as rainwater leaching and freeze-thaw cycles, the curing efficiency significantly decreases, posing a risk of secondary leaching. Furthermore, the synergistic effect between ISS and the anti-hard water agent is insufficient, limiting the curing efficiency. The anti-hard water agent, sodium dodecyl diphenyl ether disulfonate, preferentially binds with Ca in the system. 2+ Mg 2+ The combination of these factors will compete with the ISS for adsorption sites of heavy metals, reducing the effective curing efficiency of the ISS for the target heavy metals. Although the early-strength agent triethanolamine can accelerate hydration, it may change the pH and ionic activity of the system, affecting the dissociation and complexation ability of the ISS, resulting in unstable curing effect.

[0008] In summary, although red mud-graphite tailings-based road base materials have significant ecological and economic benefits in the high-value utilization of solid waste, there is still an urgent need to address the problem of efflorescence caused by the strong alkalinity of the raw material red mud and how to effectively fix heavy metals in the material to prevent them from migrating into the soil and accumulating with the leachate. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing red mud-graphite tailings-based road base materials, namely heavy metal pollution and efflorescence, by providing an efflorescence-resistant red mud-graphite tailings road base material and its preparation method. This road base material not only solves the heavy metal pollution problem of red mud-graphite tailings-based materials but also effectively solves the problem of efflorescence in road base materials caused by red mud-graphite tailings-based materials, achieving the dual technical effects of heavy metal pollution control and material performance enhancement, while also possessing significant environmental and resource benefits.

[0010] The technical solution of this invention is as follows:

[0011] A red mud-graphite tailings road base material for preventing efflorescence comprises the following components in parts by weight: 30-45 parts red mud, 55-70 parts graphite tailings, 2-3 parts P·O 42.5 silicate cement, 3-6 parts slag powder, 8-10 parts phosphogypsum, 0.1-0.3 parts polycarboxylate superplasticizer, 0.01-0.03 parts modified MIL-101(Fe)-NH2, and 12-15 parts water.

[0012] The graphite tailings have a particle size range of 7.5-11.2 mm and a moisture content of ≤4%; the red mud has a particle size of ≤5 mm and a moisture content of ≤3%.

[0013] The modified MIL-101(Fe)-NH2 was prepared by the following steps:

[0014] First, MIL-101(Fe)-NH2 and polydimethylsiloxane were dissolved separately in a mixed solvent composed of acetone and 2-butanone, and then sonicated to obtain a MIL-101(Fe)-NH2 suspension and a polydimethylsiloxane solution, respectively. The polydimethylsiloxane was end-capped with diglycidyl ether. The raw material MIL-101(Fe)-NH2 was formed by the coordination of iron ions with 2-aminoterephthalic acid ligands.

[0015] Then, the MIL-101(Fe)-NH2 suspension was added to the polydimethylsiloxane solution, and the resulting mixed solution was stirred and dissolved.

[0016] Finally, by evaporating the solvent in an oil bath at 70°C until the volume of the mixed solution is reduced to 1 / 10 of the original volume, the concentration is stopped, the resulting solution is dried, and the modified MIL-101(Fe)-NH2 is finally obtained.

[0017] In the aforementioned red mud-graphite tailings road base material, the graphite tailings within the specified particle size range form a skeleton, which, together with the red mud filling phase of the specified particle size, forms a dense structure, effectively reducing free water in the material and increasing the particle contact area and bonding probability.

[0018] Modified MIL-101(Fe)-NH2 reacts with heavy metal ions, especially Pb, which is highly prone to migration with the leaching solution. 2+ A chelation reaction occurs between them, forming stable chemical bonds; simultaneously, the hydrophobic groups of modified MIL-101(Fe)-NH2 block the water transport channels, allowing the heavy metal ions Pb to... 2+ The leaching medium is difficult to use, and the dual mechanism effectively reduces the amount of heavy metal ions Pb. 2+ The leaching of the material effectively avoids the heavy metal pollution problem present in red mud-graphite tailings-based materials.

[0019] In addition, the modified MIL-101(Fe)-NH2 can form a water-repellent interface zone inside the matrix, which not only reduces the penetration and adsorption of water and reduces the damage of rainwater and groundwater to the base layer, but also blocks the transport of water, thereby reducing capillary tension and achieving the purpose of reducing drying shrinkage, thus inhibiting drying shrinkage deformation and cracking.

[0020] In this material system, the pH range of the red mud is 10-11. The polycarboxylate superplasticizer, modified MIL-101(Fe)-NH2 and phosphogypsum work synergistically to form a triple protection of "adsorption-solidification-barrier", which effectively solves the problem of efflorescence in the material.

[0021] Modified MIL-101(Fe)-NH2 preferentially adsorbs free alkali metal ions, and phosphogypsum then reacts with calcium ions to form a stable compound. This dual chemical locking of Ca... 2+ Reduce free Ca 2+ concentration.

[0022] The reacted ettringite and modified MIL-101(Fe)-NH2 filler synergistically reduce micron and nano-scale porosity, forming a gradient dense structure that blocks water permeation pathways. Simultaneously, the polycarboxylate superplasticizer, due to its unique comb-like molecular structure, can effectively disperse particles such as red mud and graphite tailings, significantly reducing the water-cement ratio, improving material density and impermeability, greatly hindering water and ion migration, and further suppressing capillary water transport.

[0023] In addition, the modified MIL-101(Fe)-NH2 effectively reduces water accumulation and inhibits the salt dissolution-crystallization cycle.

[0024] The combined effect of all these factors effectively solved the efflorescence problem of the red mud-graphite tailings road base material. At the same time, the overall structural density of the material was improved, and its resistance to freeze-thaw cycles and carbonization was enhanced, thus reducing the risk of long-term efflorescence from the root.

[0025] In this invention, the slag powder in the anti-efflorescence red mud-graphite tailings road base material is S95 grade blast furnace slag powder with a specific surface area of ​​483-525 m². 2 / kg, with an activity index of 96%-102% after 28 days, slag powder can work synergistically with P·O 42.5 silicate cement to physically adsorb alkali ions in red mud, thereby achieving the purpose of preventing efflorescence.

[0026] In this invention, the phosphogypsum in the red mud-graphite tailings road base material for preventing efflorescence has a fineness modulus of 2.0-2.4, a plasticity index of 14.5-16, and a moisture content of 6.0%-8.5%. Phosphogypsum can improve the microstructure and mechanical properties of the material; more importantly, the acidity of phosphogypsum can neutralize some of the alkalinity of the red mud, reducing the pH value of the mixture and decreasing its alkaline pollution to the environment; the SO4 in phosphogypsum... 2- It can effectively activate the reaction in red mud, further enhancing the stability and curing properties of the gelling agent matrix.

[0027] In this invention, the solid content of the polycarboxylate superplasticizer in the red mud-graphite tailings road base material for preventing efflorescence is 20%-30%, and the water reduction rate is 25%-35%. Polycarboxylate superplasticizer, also known as PC superplasticizer or PCE, is a high molecular polymer copolymerized from unsaturated monomers containing carboxyl groups and other monomers.

[0028] The preparation method of the above-mentioned red mud-graphite tailings road base material for preventing efflorescence includes the following steps:

[0029] (1) Raw material pretreatment:

[0030] The red mud was pretreated to control its moisture content to below 3%; the graphite tailings were pretreated to control their moisture content to below 4%.

[0031] Place the red mud in a drying device at 100-110℃ and dry for 4-6 hours until the moisture content drops below 3%. For graphite tailings, air dry naturally or dry at low temperature (drying temperature 60-80℃) to control the moisture content below 4%. If the graphite tailings are too dry, a small amount of water can be sprayed to adjust the moisture content to 2%-3%.

[0032] (2) Preparation of modified MIL-101(Fe)-NH2 dispersion:

[0033] The modified MIL-101(Fe)-NH2 was added to water accounting for 50% of the total weight of water, and then ultrasonically dispersed (power 300W-350W, time 10min-15min) to prepare a uniform modified MIL-101(Fe)-NH2 dispersion.

[0034] (3) Material mixing:

[0035] First, dry mix the red mud and phosphogypsum, then add the polycarboxylate superplasticizer and continue stirring at a speed of 60-70 r / min for 1-2 minutes.

[0036] Then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2) and stir at 60-70 r / min for 1-2 min at room temperature;

[0037] Then, graphite tailings, P·O 42.5 silicate cement, slag powder and the remaining 50% water are put into a mixer and stirred at 60-70 r / min for 2-3 minutes at room temperature to obtain the red mud-graphite tailings road base material with anti-efflorescence properties.

[0038] In the preparation method provided by the present invention, ultrasonic dispersion is used to make the modified MIL-101(Fe)-NH2 more uniformly dispersed, avoiding the agglomeration of the modified MIL-101(Fe)-NH2 material, and further ensuring that the modified MIL-101(Fe)-NH2 material can play a full role in the red mud-graphite tailings road base.

[0039] This invention also provides the application of the above-mentioned red mud-graphite tailings road base material, specifically for the base construction of Class II and above highways.

[0040] The beneficial effects of this invention are as follows: The red mud-graphite tailings road base material for preventing efflorescence described in this invention not only solves the heavy metal pollution problem of red mud-graphite tailings base material, but also effectively solves the problem that red mud-graphite tailings base material is prone to causing efflorescence in road base, achieving the dual technical effects of heavy metal pollution control and material performance enhancement, while also possessing significant environmental and resource benefits.

[0041] In the red mud-graphite tailings road base material system of the present invention, the graphite tailings within the specified particle size range form a skeleton, which, together with the red mud filling phase of the specified particle size, forms a dense structure, effectively reducing free water in the material and increasing the particle contact area and bonding probability.

[0042] Modified MIL-101(Fe)-NH2 reacts with heavy metal ions, especially Pb, which is highly prone to migration with the leaching solution. 2+ A chelation reaction occurs between them, forming stable chemical bonds, thereby solidifying lead ions in the material system and mitigating ecological risks. Simultaneously, the hydrophobic groups of the modified MIL-101(Fe)-NH2 block moisture transport channels, improving the water stability of the red mud-graphite tailings base material; more importantly, it enables the release of heavy metal ions (Pb)... 2+ The leaching medium is difficult to use, and the dual mechanism effectively reduces the amount of heavy metal ions Pb. 2+ The leaching of the material effectively avoids the heavy metal pollution problem present in red mud-graphite tailings-based materials.

[0043] In addition, the modified MIL-101(Fe)-NH2 can form a water-repellent interface zone inside the matrix, which not only reduces the penetration and adsorption of water and reduces the damage of rainwater and groundwater to the base layer, but also blocks the transport of water, thereby reducing capillary tension and achieving the purpose of reducing drying shrinkage, thus inhibiting road surface shrinkage deformation and cracking.

[0044] In this material system, the pH range of the red mud is 10-11. The polycarboxylate superplasticizer, modified MIL-101(Fe)-NH2 and phosphogypsum work synergistically to form a triple protection of "adsorption-solidification-barrier", which effectively solves the problem of efflorescence in the material.

[0045] Modified MIL-101(Fe)-NH2 preferentially adsorbs free alkali metal ions, and phosphogypsum then reacts with calcium ions to form a stable compound. This dual chemical locking of Ca... 2+ Reduce free Ca 2+ concentration.

[0046] The reacted ettringite and modified MIL-101(Fe)-NH2 filler synergistically reduce micron and nano-scale porosity, forming a gradient dense structure that blocks water permeation pathways. Simultaneously, the polycarboxylate superplasticizer, due to its unique comb-like molecular structure, can effectively disperse particles such as red mud and graphite tailings, significantly reducing the water-cement ratio, improving material density and impermeability, greatly hindering water and ion migration, and further suppressing capillary water transport.

[0047] In addition, the modified MIL-101(Fe)-NH2 effectively reduces water accumulation and inhibits the salt dissolution-crystallization cycle.

[0048] The combined effect of all these factors effectively solved the efflorescence problem of the red mud-graphite tailings road base material. At the same time, the overall structural density of the material was improved, and its resistance to freeze-thaw cycles and carbonization was enhanced, thus reducing the risk of long-term efflorescence from the root.

[0049] The 7-day unconfined compressive strength range of the red mud-graphite tailings road base material for preventing efflorescence described in this invention is 4.9-7.9 MPa. Detailed Implementation

[0050] The technical solution of the present invention will be described in detail below.

[0051] 1. In the following examples and comparative examples, the graphite tailings were sourced from the Pingdu section of National Highway 206 in Shandong Province; the red mud was sourced from the accumulated waste red mud in Zibo City; the cement used was P·O 42.5 silicate cement produced by Shandong Cement Plant; the slag powder was sourced from Laiwu Branch of Shandong Iron and Steel Co., Ltd.; and the phosphogypsum was sourced from Jinan Cement Plant.

[0052] All other experimental reagents are standard commercially available reagents and will not be described in detail here.

[0053] 2. The experimental procedure was carried out in accordance with the "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering" (JTGE51-2009).

[0054] The loss rate of compressive strength (BDR) is the ratio of the compressive strength of the specimen before and after freeze-thaw.

[0055] The 7-day unconfined compressive strength was determined by curing the specimens in a standard curing chamber for 6 days, with the last day being water immersion curing.

[0056] The water stability coefficient is the ratio of the saturated compressive strength of the specimen to its dry compressive strength.

[0057] The curing period for 30-day dry shrinkage strain specimens is generally 7 days, with the specimens saturated with water for 24 hours on the last day of the curing period.

[0058] The leaching of heavy metal ions was carried out in accordance with the "Determination of Leachable Heavy Metals in Cement Mortar" (GB / T 30810-2014), and the heavy metal ions to be determined were lead ions.

[0059] 3. The modified MIL-101(Fe)-NH2 used in the material system is prepared through the following steps:

[0060] First, 0.2 g of MIL-101(Fe)-NH2 and 1.2 g of polydimethylsiloxane were dissolved in 40 mL of a mixed solvent of acetone and 2-butanone (acetone:2-butanone volume ratio of 100:1) and subjected to sonication for 10 min. The polydimethylsiloxane was end-capped with diglycidyl ether.

[0061] Then, the MIL-101(Fe)-NH2 suspension was added to the polydimethylsiloxane solution, and the resulting mixture was stirred at 40°C at a stirring speed of 500-1000 rpm for at least 20 hours to ensure complete dissolution.

[0062] Finally, the solvent was evaporated in a 70°C oil bath until the volume of the mixed solution was reduced to 1 / 10 of the original volume. Concentration was then stopped, and the resulting solution was dried in a 60°C vacuum drying oven for 24 hours to finally obtain modified MIL-101(Fe)-NH2.

[0063] 4. The graphite tailings used in the material systems described in Examples 1-3 have a particle size range of 7.5-11.2 mm and a moisture content of ≤4%; the red mud has a particle size of ≤5 mm and a moisture content of ≤3%.

[0064] Example 1

[0065] The red mud-graphite tailings road base material for preventing efflorescence comprises the following components in parts by weight: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 9 parts phosphogypsum, 0.2 parts polycarboxylate superplasticizer, 0.02 parts modified MIL-101(Fe)-NH2, and 13.5 parts water.

[0066] The phosphogypsum has a fineness modulus of 2.05, a plasticity index of 14.9, and a moisture content of 6.3%.

[0067] The blast furnace slag powder is S95 grade, with a specific surface area of ​​524.14 m². 2 / kg, 28d activity index 96%.

[0068] The preparation method of the red mud-graphite tailings road base material for preventing efflorescence includes the following specific steps:

[0069] (1) Raw material pretreatment:

[0070] Place the red mud and graphite tailings in a drying device at 110℃ and dry for 4 hours until the moisture content drops below 3%. If it is too dry, a small amount of water can be sprayed to adjust the moisture content to 3%.

[0071] (2) Preparation of dispersion:

[0072] 0.2g of modified MIL-101(Fe)-NH2 was added to 67.5g of water and then ultrasonically dispersed at 300W for 10min to prepare a uniform modified MIL-101(Fe)-NH2 dispersion.

[0073] (3) Material mixing:

[0074] First, dry mix 380g of red mud and 90g of phosphogypsum in a mixer, then add 2g of polycarboxylate superplasticizer and stir at 60r / min for 1min at room temperature.

[0075] Then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2) and stir at 60 r / min for 2 min at room temperature.

[0076] Then, 620g of graphite tailings, 25g of P·O 42.5 silicate cement, 45g of slag powder and the remaining 67.5g of water are put into a mixer and stirred at 60r / min for 2min to obtain the red mud-graphite tailings road base material with anti-efflorescence properties.

[0077] Example 2

[0078] The red mud-graphite tailings road base material for preventing efflorescence comprises the following components in parts by weight: 45 parts red mud, 55 parts graphite tailings, 3 parts P·O 42.5 silicate cement, 6 parts slag powder, 10 parts phosphogypsum, 0.3 parts polycarboxylate superplasticizer, 0.03 parts modified MIL-101(Fe)-NH2, and 15 parts water.

[0079] The others are the same as in Example 1.

[0080] Example 3

[0081] The red mud-graphite tailings road base material for preventing efflorescence comprises the following components in parts by weight: 30 parts red mud, 70 parts graphite tailings, 2 parts P·O 42.5 silicate cement, 3 parts slag powder, 8 parts phosphogypsum, 0.1 parts polycarboxylate superplasticizer, 0.01 parts modified MIL-101(Fe)-NH2, and 12 parts water.

[0082] The others are the same as in Example 1.

[0083] Comparative Example 1

[0084] The difference from Example 1 is that the red mud-graphite tailings road base material described in this comparative example did not contain modified MIL-101(Fe)-NH2.

[0085] Specifically, it is composed of the following components in the indicated weight proportions: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 9 parts phosphogypsum, 0.2 parts polycarboxylate superplasticizer, and 13.5 parts water.

[0086] The others are the same as in Example 1.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that the modified MIL-101(Fe)-NH2 in the red mud-graphite tailings road base material is replaced with MIL-101(Fe)-OH.

[0089] Specifically, it consists of the following components in the indicated weight proportions: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 9 parts phosphogypsum, 0.2 parts polycarboxylate superplasticizer, 0.02 parts MIL-101(Fe)-OH, and 13.5 parts water.

[0090] The others are the same as in Example 1.

[0091] Comparative Example 3

[0092] The difference from Example 1 is that the modified MIL-101(Fe)-NH2 in the red mud-graphite tailings road base material is replaced with MIL-125(Ti).

[0093] It is composed of the following components in the indicated weight proportions: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 9 parts phosphogypsum, 0.2 parts polycarboxylate superplasticizer, 0.02 parts MIL-125(Ti), and 13.5 parts water.

[0094] The others are the same as in Example 1.

[0095] Comparative Example 4

[0096] The difference from Example 1 is that the red mud and graphite tailings in the red mud-graphite tailings road base material described in this comparative example have a particle size of ≤5mm.

[0097] The others are the same as in Example 1.

[0098] Comparative Example 5

[0099] The difference from Example 1 is that the phosphogypsum in the red mud-graphite tailings road base material is replaced with desulfurized gypsum.

[0100] Specifically, it consists of the following components in the indicated weight proportions: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 9 parts desulfurized gypsum, 0.2 parts polycarboxylate superplasticizer, 0.02 parts modified MIL-101(Fe)-NH2, and 13.5 parts water.

[0101] The others are the same as in Example 1.

[0102] Comparative Example 6

[0103] The difference from Example 1 is the amount of phosphogypsum and modified MIL-101(Fe)-NH2 added.

[0104] The red mud-graphite tailings road base material described in the comparative example is composed of the following components in parts by weight: 38 parts red mud, 62 parts graphite tailings, 2.5 parts P·O 42.5 silicate cement, 4.5 parts slag powder, 12 parts phosphogypsum, 0.2 parts polycarboxylate superplasticizer, 0.06 parts modified MIL-101(Fe)-NH2, and 13.5 parts water.

[0105] The others are the same as in Example 1.

[0106] Comparative Example 7

[0107] The difference from Example 1 is the order in which the phosphogypsum is added in step (3).

[0108] Step (3) in the preparation method of the red mud-graphite tailings road base material described in this comparative example is as follows:

[0109] First, add 2g of polycarboxylate superplasticizer to 380g of red mud and stir at 60r / min for 1min at room temperature.

[0110] Then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2) and stir at 60 r / min for 2 min at room temperature.

[0111] Then, add 620g of graphite tailings, 90g of phosphogypsum, 25g of P·O 42.5 silicate cement, 45g of slag powder and the remaining 67.5g of water into a mixer and stir at 60r / min for 2min to obtain red mud-graphite tailings road base material.

[0112] Comparative Example 8

[0113] The difference from Example 1 is the order in which the water-reducing agent and the modified MIL-101(Fe)-NH2 are added in step (3).

[0114] Step (3) in the preparation method of the red mud-graphite tailings road base material described in this comparative example is as follows:

[0115] First, dry mix 380g of red mud and 90g of phosphogypsum in a mixer, then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2), and stir at 60r / min for 1min at room temperature.

[0116] Then, add 620g of graphite tailings, 25g of P·O 42.5 silicate cement, 45g of slag powder and the remaining 67.5g of water into the mixer and mix at 60r / min for 2min.

[0117] Finally, add 2g of polycarboxylate superplasticizer and stir at 60r / min for 2min at room temperature to obtain red mud-graphite tailings road base material.

[0118] Table 1 Performance indicators of road materials obtained from each embodiment and comparative example.

[0119]

[0120] As shown in Table 1, the 7-day unconfined compressive strength of Examples 1-3 is greater than 2.0 MPa, which meets the strength requirement of not less than 2.0 MPa for cement-fly ash stabilized materials as base course in the "Specifications for Design of Highway Asphalt Pavement" JTGD50-2017.

[0121] In Comparative Example 1, the 7-day unconfined compressive strength did not meet the strength requirements, and the BDR value was low. It also exhibited poor frost resistance and water stability, indicating that the lack of modified MIL-101(Fe)-NH2 to block moisture in this comparative example failed to inhibit material shrinkage. Furthermore, Comparative Example 1 showed a high lead content, indicating the absence of modified MIL-101(Fe)-NH2 to solidify heavy metal ions. The lack of modified MIL-101(Fe)-NH2 also resulted in weak resistance to efflorescence, with severe efflorescence accompanied by powdering, demonstrating that modified MIL-101(Fe)-NH2 plays a significant role in preventing efflorescence.

[0122] In Comparative Example 2, after replacing the modified MIL-101(Fe)-NH2 with MIL-101(Fe)-OH, the unconfined compressive strength and BDR at 7d decreased significantly, the dry shrinkage strain at 30d reached its peak, and the lead ion content surged. This indicates that MIL-101(Fe)-OH has a counterproductive effect on strength, and that MIL-101(Fe)-OH has poor selectivity for lead ions and cannot adsorb lead ions.

[0123] In Comparative Example 3, after the modified MIL-101(Fe)-NH2 was replaced with MIL-125(Ti), similar to Comparative Example 2, the unconfined compressive strength at 7d was significantly reduced, the shrinkage strain at 30d was increased, and the lead ion content exceeded the standard. It can be seen that only the modified MIL-101(Fe)-NH2 has the strongest selectivity for lead ions and has a positive effect on strength.

[0124] In Comparative Example 4, the particle size of both red mud and graphite tailings was ≤5mm. The 7-day unconfined compressive strength and BDR were significantly reduced. Due to the lack of corresponding coarse and fine aggregates, the gradation was poor, the strength was reduced, and the 30-day drying shrinkage strain was increased.

[0125] In Comparative Example 5, after replacing phosphogypsum with desulfurized gypsum, the synergistic reaction between desulfurized gypsum and red mud exacerbated the efflorescence of red mud, resulting in reduced strength, greater shrinkage, and poor efflorescence prevention, which does not meet the requirements of green development.

[0126] In Comparative Example 6, the phosphogypsum and modified MIL-101(Fe)-NH2 exceeded the range defined in this invention, resulting in reduced strength and BDR, large shrinkage, high lead ion content, and poor alkali resistance. It can be seen that the content is not necessarily better the higher it is, but should be within a reasonable range.

[0127] In Comparative Example 7, the order of adding phosphogypsum was changed, and in Comparative Example 8, the order of adding polycarboxylate superplasticizer was changed. Compared with Example 1, the strength and BDR were still reduced, the shrinkage was large, the lead ion content was high, and the anti-alkali efflorescence was poor. The order defined in this invention is the optimal order.

Claims

1. A red mud-graphite tailings road base material for preventing efflorescence, characterized in that, The composition includes the following components in parts by weight: 30-45 parts red mud, 55-70 parts graphite tailings, 2-3 parts P·O 42.5 silicate cement, 3-6 parts slag powder, 8-10 parts phosphogypsum, 0.1-0.3 parts polycarboxylate superplasticizer, 0.01-0.03 parts modified MIL-101(Fe)-NH2, and 12-15 parts water. The particle size range of the graphite tailings is 7.5-11.2 mm, and the particle size of the red mud is ≤5 mm; The modified MIL-101(Fe)-NH2 was prepared by the following steps: First, MIL-101(Fe)-NH2 and polydimethylsiloxane were dissolved in a mixed solvent composed of acetone and 2-butanone, respectively, and ultrasonically treated to obtain MIL-101(Fe)-NH2 suspension and polydimethylsiloxane solution, respectively. Then, the MIL-101(Fe)-NH2 suspension was added to the polydimethylsiloxane solution, and the resulting mixed solution was stirred and dissolved. Finally, by evaporating the solvent in an oil bath at 70°C until the volume of the mixed solution is reduced to 1 / 10 of the original volume, the concentration is stopped, the resulting solution is dried, and the modified MIL-101(Fe)-NH2 is finally obtained. The aforementioned red mud-graphite tailings road base material for preventing efflorescence is prepared through the following steps: (1) Raw material pretreatment: The red mud was pretreated to control its moisture content to below 3%; the graphite tailings were pretreated to control their moisture content to below 4%. (2) Preparation of modified MIL-101(Fe)-NH2 dispersion: The modified MIL-101(Fe)-NH2 was added to water accounting for 50% of the total weight of water, and then ultrasonically dispersed to prepare a uniform modified MIL-101(Fe)-NH2 dispersion. (3) Material mixing: First, dry mix the red mud and phosphogypsum, then add the polycarboxylate superplasticizer and continue stirring at a speed of 60-70 r / min for 1-2 minutes. Then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2) and stir at 60-70 r / min for 1-2 min at room temperature; Then, graphite tailings, P·O 42.5 silicate cement, slag powder and the remaining 50% water are put into a mixer and stirred at 60-70 r / min for 2-3 minutes at room temperature to obtain the red mud-graphite tailings road base material with anti-efflorescence properties.

2. The red mud-graphite tailings road base material for preventing efflorescence according to claim 1, characterized in that, The slag powder mentioned is S95 grade blast furnace slag powder.

3. The red mud-graphite tailings road base material for preventing efflorescence according to claim 2, characterized in that, The specific surface area of ​​the S95 grade blast furnace slag powder is 483-525 m². 2 / kg, with an activity index of 96%-102% after 28 days.

4. The red mud-graphite tailings road base material for preventing efflorescence according to claim 1, characterized in that, The phosphogypsum has a fineness modulus of 2.0-2.4, a plasticity index of 14.5-16, and a moisture content of 6.0%-8.5%.

5. The red mud-graphite tailings road base material for preventing efflorescence according to claim 1, characterized in that, The polycarboxylate superplasticizer has a solid content of 20%-30% and a water reduction rate of 25%-35%.

6. The method for preparing the red mud-graphite tailings road base material for preventing efflorescence as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Raw material pretreatment: The red mud was pretreated to control its moisture content to below 3%; the graphite tailings were pretreated to control their moisture content to below 4%. (2) Preparation of modified MIL-101(Fe)-NH2 dispersion: The modified MIL-101(Fe)-NH2 was added to water accounting for 50% of the total weight of water, and then ultrasonically dispersed to prepare a uniform modified MIL-101(Fe)-NH2 dispersion. (3) Material mixing: First, dry mix the red mud and phosphogypsum, then add the polycarboxylate superplasticizer and continue stirring at a speed of 60-70 r / min for 1-2 minutes. Then add the modified MIL-101(Fe)-NH2 dispersion prepared in step (2) and stir at 60-70 r / min for 1-2 min at room temperature; Then, graphite tailings, P·O 42.5 silicate cement, slag powder and the remaining 50% water are put into a mixer and stirred at 60-70 r / min for 2-3 minutes at room temperature to obtain the red mud-graphite tailings road base material with anti-efflorescence properties.

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